The invention relates to a steam iron comprising a steam chamber which is provided with a hydrophilic coating. The invention further relates to a method of providing a hydrophilic coating in the steam chamber of a steam iron.
Present day steam irons comprise a water reservoir from which water is fed at an adjustable and regular rate to the steam chamber. Said steam chamber is partly located in the part of the steam iron to be heated, namely the soleplate of the iron. In the steam chamber the water is converted into steam after which said steam is fed outwards through steam ports in the soleplate of the iron.
In general, the steam chamber is bounded by metal walls which are generally composed of aluminum. When water is fed from the reservoir directly onto the hot metal bottom of the steam chamber the so-called "Leiden-frost" effect occurs: the water is not optimally distributed over the bottom surface and remains bouncing about on the surface in the form of large drops; it is even possible for these drops to fly off the surface, pass through the steam chamber and leave the iron through the steam ports. In such a situation, the formation of steam is not optimal. In order to preclude this undesirable effect a hydrophilic and moderate heat-insulating coating is customarily applied to at least the bottom of the steam chamber. By virtue of the hydrophilic character of the steam chamber coating the water introduced spreads readily over the bottom of the steam chamber. The moderate heat-insulating character of the layer ensures a gradual heat transfer from the soleplate of the iron to the water that is introduced. Both properties of the steam chamber coating contribute to the water being regularly and efficiently converted into steam.
A steam iron of the type described in the opening paragraph is known from, inter alia, British Patent Specification GB 773,741. The steam chamber coating used in this patent specification is mainly composed of silica and fillers which are provided on the bottom of the steam chamber from an alkaline colloidal suspension, preferably, by means of a spraying process. According to this patent specification, a steam chamber coating having optimum properties is obtained when the colloidal suspension is stabilised with NaOH in the range from pH 9.5-10.5.
Applicants have ascertained that the known steam iron has disadvantages. For example, it has been found that corrosion problems occur, in particular, in an environment having a high degree of humidity and a relatively high temperature. This causes flakes to break away from the steam chamber coating which can leave the iron through the steam ports. This situation is found to be very disadvantageous.